As textile substrates age, their color tends to fade or yellow due to exposure to light, air, soil, and natural degradation of the fibers that comprise the substrates. As such, to visually enhance these textile substrates and counteract the fading and yellowing the use of polymeric colorants for coloring consumer products has become well known in the prior art. For example, it is well known to use whitening agents, either optical brighteners or bluing agents, in textile applications. However, traditional whitening agents tend to lose efficacy upon storage due to deleterious interactions with other formulation components (such as, for example, perfumes). As such, formulators tend to increase the level of whitening agent used to counteract any efficacy lost upon storage.
Leuco dyes are also known in the prior art to exhibit a change from a colorless or slightly colored state to a colored state upon exposure to specific chemical or physical triggers. The change in coloration that occurs is typically visually perceptible to the human eye. All existing compounds have some absorbance in the visible light region (400-750 nm), and thus more or less have some color. In this invention, a dye is considered as a “leuco dye” if it did not render a significant color at its application concentration and conditions, but renders a significant color in its triggered form. The color change upon triggering stems from the change of the molar attenuation coefficient (also known as molar extinction coefficient, molar absorption coefficient, and/or molar absorptivity in some literatures) of the leuco dye molecule in the 400-750 nm range, preferably in the 500-650 nm range, and most preferably in the 530-620 nm range. The increase of the molar attenuation coefficient of a leuco dye before and after the triggering should be bigger than 50%, more preferably bigger than 200%, and most preferably bigger than 500%.
As such, there remains a need for an effective whitening agent that increases efficacy upon storage, rather than degrade and loose efficacy.
It has now surprisingly been found that the presently claimed leuco colorants not only provide the desired consumer whiteness benefit, but detergents containing these colorants deliver increasing whiteness upon storage. Therefore, the presently claimed laundry care compositions actually become more effective the longer they are stored and eliminate the need for formulators to add unnecessary and wasted levels of whitening agent to counteract the amount lost upon storage or to compensate for loss of cleaning power over time due to the degradation of other cleaning components (such as enzymes, for example).